VDF is a useful monomer in the preparation of fluorocarbon polymers which have excellent weathering and chemical resistance properties. A copending application filed on even date herewith, attorney docket number IR 3245, describes a process for the gas phase catalytic hydrofluorination of vinylidene chloride ("VDC") to yield a product stream rich in 1-chloro-1,1-difluoroethane ("142b"), 1,1-dichloro-1-fluoroethane ("141b"), HCl, and 143a, and the subsequent conversion of the resulting 142b and HCl to VDF. Since 143a is a by-product of the catalytic hydrofluorination step, it would be desirable to also have a viable process for directly converting impure 143a/HCl product mixtures into VDF.
Several processes have been reported for converting pure 143a (specifically or generically) into VDF monomer [U.S. Pat. Nos. 2,461,523; 2,442,993; and 3,456,025; F. H. Walker et al., J. Org. Chem., 30, p. 3284 (1965); and Japanese Patent Application 54-130507].
The presence of HCl in the process of this invention makes the result unpredictable. For example, it is known that HCl can be readily oxidized with air to form chlorine gas [C. N. Satterfield, Heterogeneous Catalysis in Practice, McGraw Hill (1980) 206-208] and, subsequently, that the chlorine generated can be used to chlorinate the methyl group of 143a [M. Hudlicky, Chemistry of Organic Fluorine Compounds, Ellis Horwood Limited (1976) 218] to form 1,1,1-trifluoro-2-chloroethane, which in turn can be dehydrofluorinated into 1,1-difluoro-2-chloroethylene. These products can not be readily converted back into 143a or VDF.